1. Field of the Invention
This invention relates to a method of estimating deterioration of a light emitting device used in a magneto-optical recording/reproducing system using a magneto-optic disc, and a light emission driving apparatus employing the method.
2. Description of the Related Art
In a magneto-optical recording/reproducing system using a magneto-optic disc, for example, a laser diode (LD) using a semiconductor, etc. is used as a light emitting device of optical pickup means. The laser diode is excited (driven) by a driving signal which is based on data supplied from driving means associated therewith, to provide a predetermined light output. The predetermined output light is irradiated onto a magneto-optic disc to record data thereon, and another predetermined output light is irradiated onto the magneto-optic disc to read out data recorded thereon.
The laser diode deteriorates with time, and after being used longer than a certain period of time, it fails to provide the required light output. Specifically, as shown in FIG. 6, a driving current I required to obtain an identical light output Pw tends to rise with an increase in the amount t of time used, and the light output shows a tendency to sharply drop when a certain driving current is exceeded.
Therefore, some laser diode makers employ a policy to specify the term of guarantee, with a view to warning that the laser diode should be replaced when the term of guarantee has elapsed. Depending on users, on the other hand, they may continue to use a laser diode and replace it only when data recording becomes unavailable.
The term of guarantee is set taking account of variations of individual laser diodes. Thus, some laser diodes are fully usable even after the term of guarantee has expired, and in this case, the term setting merely forces wasteful and uneconomical use of laser diodes.
In the case of replacing a laser diode only when data recording becomes unavailable, the laser diode can be used up, but there is a possibility that the service life of the laser diode suddenly comes to an end and fails to emit light with sufficient intensity while data is actually recorded or reproduced. If this occurs, it is necessary to check, for example, recorded data again to determine to which point data has been effectively recorded, requiring much labor.